Chronic hypoxia induces dramatic fibro-proliferative remodeling in the pulmonary artery (PA)adventitia that is especially impressive during the neonatal period and clearly contributes to the marked increase in pulmonary vascular resistance observed. One of the key mediators of these responses is protein kinase C (PKC) [unreadable] (zeta) which regulates hypoxia-inducible genes. To study the adventitial remodeling, we used PA adventitial fibroblasts cultured from neonatal control (Fib-C) and hypoxic pulmonary hypertensive calves (Fib-H) and compared the effects of hypoxia on PKC[unreadable]-related signaling pathways. We have observed that acute hypoxic exposure induces translocation of nuclear PKC[unreadable] into the nuclear membrane and the cytoplasm selectively in Fib-C, but not in Fib-H. In Fib-C, PKG;inhibition results in sustained activation of extracellular signal-regulated kinases, ERK1/2, whereas it blocks ERK1/2 activation in Fib-H. The mechanisms by which PKC[unreadable] can diversify its own biochemical properties in response to chronic hypoxia remain unexplored. Although PKC[unreadable] suppresses the hypoxia-induced proliferation of Fib-C, it translates the hypoxic signal into replicative responses in Fib-H. The molecular mechanisms that confer the ability of PKC[unreadable] to perform opposing functions, especially in proliferative responses, are unknown and will be examined here. We also found that PKC^ regulates MAP kinase phosphatase-1 (MKP-1) expression only in Fib-C, but not in Fib-H. The biochemical pathways responsible for uncoupling of PKQ;from the regulation of MKP-1 expression in Fib-H are not known. The aforementioned questions will be addressed by the following specific aims: 1) The development of hypoxic pulmonary hypertension leads to the appearance of fibroblasts with modified nuclear localization, activation and target specificity of PKC[unreadable];2) An altered functional role of PKC[unreadable] as a growth regulator, promotes enhanced proliferation of fibroblasts from chronically hypoxic animals;3) Nuclear PKC^-mediated growth-suppressing activity of MKP-1 is absent in fibroblasts isolated from the adventitial compartment of chronically hypoxic animals. Successful completion of the proposed experiments will provide new insights into the role of PKCf;and MKP-1 in pulmonary vascular diseases and could lead to the development of improved therapeutic strategies for the treatment of pulmonary diseases caused by chronic hypoxia.